Flume test on mechanical responses of wind-wave cyclic loaded offshore wind turbine supported by jacket foundation considering time-varied local scour effects

Large diameter pile (LDP) jacket foundations have recently seen increased application in offshore wind energy engineering due to their ability to avoid the complexities of rock-socketed pile construction. Offshore wind turbines (OWTs) supported by LDP-jacket foundations are subjected to long-term wind-wave loading and local scour caused by ocean currents after installation, posing challenges to their structural service performance. This paper presents an experimental study by using two compact cyclic loading devices to simulate long-term wind and wave cyclic loading with different characteristics at various heights. Additionally, stable unidirectional flow is generated in the test area by the flume to achieve the combined effects of long-term cyclic loading and time-varying scour processes. The experimental study investigates the mechanical responses of the LDP-jacket foundation supported OWT system under these combined effects, including the cumulative deformation of the structure, the ultimate bearing capacity, and the migration of the natural frequency of the OWT system. Comparisons are made with scenarios considering only solely environmental factors. The results of this study can be used to predict the service performance evolution of newly installed LDP-jacket supported OWTs more accurately.